1. Field of the Invention
The present invention relates to a semiconductor processing apparatus and, particularly to a CVD (Chemical Vapor Deposition) apparatus for processing a semiconductor wafer while being optically heated.
2. Description of the Related Art
In a manufacturing process of a semiconductor device, a sputter apparatus and a CVD apparatus are used, and a thin film is formed on a semiconductor wafer. In such a film forming process, in order to uniformly grow the thin film on the wafer, it is important to heat and maintain an entire surface of the wafer at a predetermined temperature. A heating method can be roughly classified to heating by a heater and heating by an energy line, e.g., light of a lamp. The lamp heating is often used in a semiconductor manufacturing device in which an object is mounted in vacuum atmosphere since heat energy is transmitted in vacuum by radiation.
The conventional vacuum processing apparatus of lamp heating type comprises a vacuum chamber in which a mount base of a semiconductor wafer is arranged, and a heating lamp arranged outside the chamber. A wall of the chamber, which is opposite to the lamp, is formed of a window plate made of quartz glass. Light emitted from the lamp is radiated into the chamber through the window plate. The lamp is arranged to heat the mount base, so that the wafer on the mount base is heated over the entire surface from the rear surface.
An exhaust pump and a process gas source are connected to the vacuum chamber, and a predetermined vacuum atmosphere is given to the vacuum chamber, and process gas is supplied thereto.
Published Unexamined Japanese Patent Application No. 58-164222 discloses a processing apparatus of an infrared lamp heating type.
In the above apparatus, by-products are deposited on the inside of a window plate, so that a film can be easily formed. If such a film is formed, transmitted light is absorbed by the film, and the window plate is heated by absorption light through the film. If this process is repeated, the thickness of the film, which is deposited on the window plate, is increased, and a heating rate of the window plate is increased. In other words, the rate of the rise in temperature of the window plate during the process is also increased.
Even if the window plate is periodically cleaned, light transmissivity of quartz glass, which is altered and weakened by heating, cannot be recovered. In other words, only by removing the film from the surface of the window plate, it is difficult to recover light transmissivity of the window plate and to prevent the window plate from being heated. Inventors of the present invention have found out a problem such that if the window glass of quartz glass is periodically cleaned and continuously used, the window plate is finally broken and a clean room, in which the apparatus is arranged, is contaminated.